1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device that allows bias-aging even after spreading silicon over an on/off pad.
2. Discussion of the Related Art
Generally, a liquid crystal display LCD device is a representative flat panel display device that displays a picture by adjusting the transmittance of a light beam corresponding to a video signal. Particularly, the liquid crystal display device is on a trend of its application scope being broadened due to characteristics such as lightness, thinness, lower power consumption drive and the like. According to such a trend, the liquid crystal display device is used in office automation devices and the display devices of notebook computers. Further, the liquid crystal display device has been developed in a direction of wide screen, high definition and low power consumption in response to the needs of users, thereby having rapidly replaced a cathode ray tube in many application fields. Particularly, an active matrix type liquid crystal display device that drives liquid crystal cells using thin film transistors TFTs as switches has an advantage in that its picture quality is excellent and its power consumption is low, and due to the result of research and development and the use of mass production technology, the liquid crystal display device has rapidly been developed to be of large size and high resolution.
The active matrix type liquid crystal display device includes a liquid crystal display panel including liquid crystal cells arranged in an active matrix pattern; and drive circuits for driving the liquid crystal display panel. The liquid crystal display panel includes thin film transistors as a switching device for driving each of the liquid crystal cells. The thin film transistors can be an amorphous type thin film transistor using amorphous silicon or a poly type thin film transistor using poly silicon. Using the poly type thin film transistor allows embedding the drive circuitry in the liquid crystal display panel by using the poly silicon having a charge mobility of about 100 times faster than that of the amorphous silicon.
Referring to FIG. 1, a fabrication process of a liquid crystal display device is briefly described in which a drive circuit is embedded in a liquid crystal display panel. First, an upper substrate 2a where a color filter, a common electrode, a black matrix and the like are formed is bonded with a lower substrate 2b where signal lines such as data lines, gate lines and the like, TFTs, pixel electrodes and the like are formed. A liquid crystal and spacers are injected thereinto through a liquid crystal injection hole, and then the liquid crystal injection hole is sealed off to form a liquid crystal display panel 2. In the liquid crystal display panel 2, the TFT turned on by the gate line has the pixel electrode charged with video signals supplied through the data line, and the light transmittance of the liquid crystal is adjusted in accordance with the video signal, thereby realizing a picture.
At this moment, the lower substrate 2b is made larger in size than the upper substrate 2a, and on/off pads 4 is mounted on the lower substrate 2b. The on/off pads 4 includes first on/off pads 4a which supply clock signals; and second on/off pads 4b which supply R, G, B signals and drive voltages.
The poly type TFT has an advantage in that its charge mobility is fast, but has a problem in that the video signals charged in the pixel electrode is discharged because the leakage current of the poly type TFT is high.
In order to solve the problem associated with high leakage current, external bias aging signals are applied through the second on/off pads 4b to the TFT during the fabrication process to give off-state voltage stress thereto, thereby reducing the leakage current. The bias aging signals are supplied by placing a pogo pin or the like, which is connected to an external signal supplier, in contact with the second on/off pad 4b. 
After the bias aging, a cell lighting inspection that checks defect pixels is carried out using signals supplied through the first and second on/off pads 4a and 4b. A repair process is employed to perform a repair on the liquid crystal display panel 2 that is repairable and to dispose of the liquid crystal display panel 2 as a waste if the liquid crystal display panel 2 is not repairable.
A drive integrated circuit (IC) 6 inclusive of a gate drive IC and a data drive IC is mounted on the lower substrate 2b of the liquid crystal display panel 2 after the inspection and repair are completed.
The gate drive IC supplies a scan signal to each of the gate lines and the data drive IC supplies a video signal to each of the data lines.
After the drive IC 6 is mounted, a printed circuit board 8 such as FPC and the like which transmits signals to the drive IC 6 is attached onto the lower substrate 2b through an anisotropic conductive film (ACF). In the printed circuit board 8 is formed a signal pad 10 for applying the signal from the system to the drive IC 6.
Silicon for protecting the drive circuit and the wire line part is spread onto the lower substrate 2b to which the printed circuit board 8 is attached. Because the drive IC 6 receives signals through a wire line, there is no problem in supplying signals to the drive IC 6 even after the protective silicon is spread. However, it is impossible to supply the bias aging signals after the protective silicon is spread onto the lower substrate 2b because the second on/off pads 4b receive the bias signals through direct contact with a pogo pin and the like. That is to say, the liquid crystal display device of the related art has a problem in that the supplying bias aging signals is impossible after the silicon is deposited even through defects such as bright defect, residual image or the like may be generated after the silicon is spread.